斩草除根 to root out the evil
Explanation
比喻彻底消灭坏人坏事，不留后患。
It means to thoroughly eliminate bad people and bad things without leaving any future troubles.
Origin Story
春秋时期，郑国和陈国发生战争。郑庄公打败了陈国。后来，郑庄公向陈国求和，陈桓公拒绝了。过了几年，郑国变得强大起来，又攻打陈国，陈国大败，邻国也没有出兵援助。人们都说陈国自作自受，这是因为他们以前做了许多坏事，没有彻底铲除恶人，留下后患，最终自食其果。这个故事告诉我们，对于坏人坏事，要斩草除根，才能彻底解决问题，否则，即使暂时平息了，以后还会死灰复燃，带来更大的麻烦。
During the Spring and Autumn Period, Zheng and Chen states were at war. Zheng Zhuanggong defeated Chen. Later, Zheng Zhuanggong asked Chen for peace, but Chen Huanggong refused. After a few years, Zheng became stronger and attacked Chen again, and Chen suffered a devastating defeat; neighboring states did not send troops to aid. People said that Chen got what it deserved because they had done many bad things before and had not completely eliminated the evil-doers, leaving future troubles, and finally suffered the consequences. This story tells us that for bad people and bad things, we must get rid of the roots of evil to solve the problem thoroughly. Otherwise, even if it is temporarily calmed down, it will be revived in the future and bring greater trouble.
Usage
比喻彻底铲除恶势力，不留后患。
It means to completely eliminate evil forces without leaving any future troubles.
Examples
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为了避免后患，我们必须斩草除根。
wèile bìmiǎn hòuhuàn, wǒmen bìxū zhǎn cǎo chú gēn
To avoid future troubles, we must root out the evil.
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这次的反腐行动，就是要斩草除根，彻底铲除腐败的土壤。
zhè cì de fǎnfǔ xíngdòng, jiùshì yào zhǎn cǎo chú gēn, chèdǐ chǎnchú fǔbài de tǔrǎng
The current anti-corruption campaign is to eradicate corruption and thoroughly eliminate the soil of corruption.